An electronic flash device includes a flash discharge tube consisting of a cylindrical glass tube provided with a pair of discharge electrodes at either end thereof and having an interior filled with a rare gas, a trigger electrode disposed outside the flash discharge tube, and a reflector disposed on a rear side of the flash discharge tube. When a high voltage is applied to the trigger electrode, and as a result, the filler gas is ionized causing an abrupt decrease of the impedance between the pair of discharge electrodes, a discharge takes place between the discharge electrodes so that the flash discharge tube generates flash light.
In some of such electronic flash devices, the trigger electrode is made of a wire disposed so as to contact an outer circumferential surface of the flash discharge tube and extend along the longitudinal direction of the flash discharge tube (e.g., see Patent Document 1). When the flash discharge tube generates flash light repeatedly in a low, the temperature of the trigger electrode increases, causing thermal expansion of the trigger electrode.
In a case where each end of the trigger electrode is fixedly secured to the outer circumferential surface of the flash discharge tube by means of a ring, band or the like to mount the trigger electrode on the flash discharge tube, the thermal expansion of the trigger electrode may cause the trigger electrode, which is originally straight, to warp, and the thermal deformation may change the contact state between the trigger electrode and the outer circumferential surface of the flash discharge tube. The change in the contact state may cause a change in the voltage applied to the filler gas from the trigger electrode, which in turn may create problems such as unstable flashing of the flash discharge tube or variation in the amount of flash light.
To address such problems, it has been proposed to divide the trigger electrode into two halves in the longitudinal direction of the flash discharge tube, and fix only one outer end of each half of the trigger electrode to the flash discharge tube while leaving the other end free to move, thereby to achieve a structure in which the thermal expansion of the trigger electrode is not restrained and thus the thermal deformation of the trigger electrode is avoided (e.g., see Patent Document 2).